Since this is a top hit on Google search for 'How to integrate Stripe to Android Studio' and since Android studio removed the import module this is how I solved the import.

Right click on the project and select > New > Module

In your directories copy contents under Stripe > Stripe folder to the module folder (You should see a newly created folder. Delete the contents of this new folder and paste the contents of Stripe > Stripe)

Back to Android Studio navigate to build.gradle under src add compile project(":stripe") under dependencies.

Refresh your gradle.

EDIT 1
Since posting this answer some changes have happened. If you would wish to add stripe into your project do so via Maven. Just add this line to your app's build.gradle inside the dependencies section: